The present invention relates to an apparatus for applying a release agent, such as silicone oil, to the fixing roll of a plain paper copying (PPC) machine.
In the conventional fixing mechanism for a PPC machine, the toner pattern transferred to copy paper is fixed to the copy paper by passing the copy paper between a heated fixing roll and an elastic pressure roll such as a rubber roll. Unfortunately, while the paper with the toner pattern is passing between the heated fixing roll and the elastic pressure roll, the paper has a tendency to stick to both of the two rolls, causing various problems such as incomplete fixing, a double image due to the adherence of toner particles to the fixing roll rather than the copy paper (this phenomenon is generally referred to as "offsetting"), and malfunction of the copying machine.
While various methods have been proposed for solving these problems, the most usual method is to apply a release agent to the fixing roll and elastic roll. However, applying a uniform coating of the release agent in the correct amount is very difficult. If the amount of the release agent is excessive, the paper may be stained. Furthermore, too rapid a consumption of the release agent requires frequent application of the agent, and if excessive amounts of the agent are present, it will solidify on the roll surface and cause problems with the copying process. If the amount of the release agent is too small, offsetting will unavoidably occur, or the resulting poor releasability from the roll surface will cause the paper to stick to the roll. Commonly used release agents are heat-resistant oils such as silicone oil.
To eliminate these defects, various release agent applicators have been proposed, but none has proved to be completely satisfactory.
The applicant previously invented a release agent applicator. The applicator of that invention assures uniform application of the release agent, requires a minimum consumption of the agent, and can be installed in a very small area. Furthermore, the applicator has a simple configuration, is very inexpensive, and can be thrown away after use.
As shown in FIGS. 1A, 1B and 2, the fixing apparatus of that invention basically consists of a fixing roll 14 and a pressure roll 15, between which the toner image is passed to be fused onto a copy paper 16. This apparatus is characterized in that a porous polyethylene tetrafluoride resin tube 7 having both ends closed is brought into contact with the fixing roll 14 in its axial direction. A release agent 6 contained in that porous resin tube oozes out through pores of the tube to apply a thin coating of the release agent onto the roll.
Since the porous tube 7 is soft, it is carried on a support 1 (FIGS. 1A and 1B) or 4 (FIG. 2). All pores of the porous tube except those in the area which acts as an outlet for the release agent are closed with fluorine rubber or another suitable material. This is done for the purpose of discharging a predetermined and uniform amount of the release agent. The porous tube 7 may be filled with the release agent 6 before the tube is nested in the support. The applicator used for the filling operation can be thrown away after use. Alternatively, the tube may be filled with the release agent through an inlet 5 after the tube is accommodated in the support.
In FIGS. 1A, 1B and 2, reference numeral 2 represents the area of the porous polyethylene tetrafluoride resin tube where the pores are closed, and 3 refers to that area of the porous polyethylene tetrafluoride resin tube where the pores are left open.
However, this apparatus is still defective in that it takes a significant amount of time to close the pores in the area of the porous tube other than that through which the release agent is to ooze out. The present inventors later invented an improved device to remedy this drawback. As shown in FIGS. 3A and 3B, that release agent applicator includes a divided-type support 21 having an opening 23 whose width A is smaller than the maximum width B of a cavity 22. The two members of the support are joined to seal both ends of a porous polyethylene tetrafluoride resin tube 20 which is or will be filled with a release agent 6 and the major portion of which is accommodated in the cavity 22, allowing the remainder to project from the opening 23 to provide a release agent outlet. The pores in that part of the porous tube other than where the release agent oozing outlet projects from the opening are closed due to a contact force between the porous tube 20 and the corresponding wall of the cavity in the support 21.
As stated above, this device exhibits excellent performance as a release agent applicator, and a device prefilled with the release agent can be thrown away after use. However, even this applicator has one problem, that is, spillage of the release agent from the outlet during the transportation of the applicator prior to its use.